Digital servo system with calibrated notch filters

Abstract

A system which calibrates notch filters in a digital servo system is presented. A notch filter can be calibrated by obtaining a frequency response curve of the digital servo system in a range of frequencies, searching the frequency response curve for at least one peak frequency, and adjusting parameters of the notch filter to filter out signals at the at least one peak frequency. The digital servo system, for example, can be a tracking servo system or a focus servo system of an optical disk drive.

1. A method of calibrating a notch filter in an optical disk drive's digital servo system, comprising:
 digitizing sensor signals from an optical pickup unit within the optical disk drive; 
 within a digital signal processor, calculating a focus error signal or a tracking error signal from versions of the digitized sensor signals; 
 perturbing the digital servo system by adjusting either the focus error signal or the tracking error signal responsive to a perturbing signal to provide an adjusted error signal; 
 obtaining a frequency response curve of the adjusted error signal within the digital servo system over a range of frequencies in response to the perturbation of the digital servo system; 
 searching the frequency response curve for at least one frequency having a peak frequency response; and 
 setting notch filter parameters of the notch filter to filter signals in the digital servo system at the at least one frequency. 
 
   
   
     2. The method of  claim 1 , wherein the digital servo system includes a focus servo system. 
   
   
     3. The method of  claim 1 , wherein the digital servo system includes a tracking servo system. 
   
   
     4. The method of  claim 1 , wherein the frequency response curve of the digital servo system is a discrete Fourier transform. 
   
   
     5. The method of  claim 1 , wherein the range of frequencies is about 3 to about 5 kHz. 
   
   
     6. A digital servo system, comprising:
 an optical pick-up unit; 
 an analog-to-digital converter coupled to receive versions of signals from detectors in the optical pick-up unit and provide digital signals; 
 a digital signal processor coupled to receive the digital signals and operable to generate a focus error signal or a tracking error signal therefrom; 
 wherein the at least one processor executes an algorithm that 
 perturbs the digital servo system by adjusting either the focus error signal or the tracking error signal responsive to a perturbing signal to provide an adjusted error signal; 
 obtains a frequency response curve of the digital servo system's adjusted error signal over a range of frequencies in response to the perturbation of the digital servo system; 
 searches the frequency response curve for at least one frequency having a peak frequency response; and 
 sets notch filter parameters of a notch filter to filter signals in the digital servo system at the at least one frequency. 
 
   
   
     7. The system of  claim 6 , wherein the digital servo system includes a focus servo system. 
   
   
     8. The system of  claim 6 , wherein the digital servo system includes a tracking servo system.